We 'normalize' the price per mhash to do exactly what you're asking, determine which algo is paying the most currently.. but I'll see about doing it in a different way since it seems to be confusing.
I was confused too and it took me a few minutes to figure out what you're doing. I think an FAQ entry on how you calculate it and what you mean by "BTC/day/scryptMhash" would be very helpful.
Till then, for everyone else who's confused:
merc82 said he's using an X11/scrypt factor of 2.9, so if I have a rig doing 1 Mh/s mining scrypt, he expects that same rig to do about 2.9 Mh/s mining X11.
Given an scrypt hashrate, to get an X11 hashrate, I'd multiply by 2.9. Whereas given an X11 hash rate, to get an scrypt hash rate, I'd divide it by 2.9. Looking at the "BTC/day/scryptMhash" value tells you if mining X11 using that same rig could be more profitable than mining scrypt.
If you're trying to figure out projected revenue using an X11 hash rate in Mh/s (from sphminer or cpuminer, doesn't matter), first divide your hash rate by 2.9, then multiply by the "BTC/day/scryptMhash" value.